It is often desirable to provide an indication and to take remedial action when a leak of a predetermined magnitude develops in a hydraulic system. Such leak detection is particularly important in hydraulic systems used to position the control surfaces of an aircraft. In such aircraft applications, if a leak of a predetermined magnitude develops in one of the hydraulic systems of the aircraft, such systems may be shut off from the source of hydraulic fluid under pressure to prevent loss of hydraulic fluid. A hydraulic circuit breaker is utilized to accomplish this leak detection and shut off function.
In a typical aircraft hydraulic control system, hydraulic fluid is supplied to and returned from a hydraulic device. In a system of this type, the return flow is a function of the supply flow if there is no leakage in the system. Accordingly, leak detection for this type of system can be accomplished by comparing the supply and return flows.
A hydraulic circuit breaker for accomplishing this leak detection and shut off function is disclosed in Hsien Bing Wang pending U.S. patent application Ser. No. 250,398, filed Apr. 2, 1981, the entirety of which is incorporated herein by reference. As disclosed in the Wang application, a single slide valve is utilized to maintain the pressure drop across supply and return orifices substantially constant, and also to close the supply and return orifices in response to a leak of a predetermined magnitude. When it is necessary to restart the hydraulic system after the hydraulic circuit breaker shown in the Wang patent application has moved to its shut off position, it is necessary to pressurize the hydraulic circuit breaker to position the hydraulic circuit breaker in a reset mode. Devices for providing this reset pressurization may utilize an operator controlled valve for providing this reset pressure signal to the circuit breaker.
Another arrangement for resetting a hydraulic circuit breaker is shown in Frank Byford U.S. Pat. No. 3,685,531. This arrangement utilizes an accumulator piston to provide a predetermined volume of fluid under pressure to the hydraulic system. If there is no leakage in the system, this volume of fluid under pressure will pressurize the hydraulic system and reset the circuit breaker.